Multifractal intermittency of Eulerian and Lagrangian turbulence of ocean temperature and plankton fields

Nonlinear Processes in Geophysics - Tập 3 Số 4 - Trang 236-246
Laurent Seuront1, François G. Schmitt2,3, Daniel Schertzer2, Yvan Lagadeuc1, S. Lovejoy4
1Station Marine de Wimereux, CNRS-URA 1363, Université des Sciences et Technologie de Lille, 28 avenue Foch, BP 80, 62930 Wimereux, France
2Laboratoire de Météorologie Dynamique, CNRS/UPR 1211, Université Pierre et Marie Curie, Tour 15, BP 99, 4 place Jussieu, 75252 Paris Cedex 05, France
3now at the Institut Royal Météorologique, Section Climatologie Dynamique, 3 avenue Circulaire, 1180 Bruxelles, Belgium
4Physics Dept., McGill University, 3600 University St., Montréal, H3A 2T8, Canada

Tóm tắt

Abstract. In this paper, we present evidence that intermittency of Eulerian and Lagrangian turbulence of ocean temperature and plankton fields is multifractal and furthermore can be analysed with the help of universal multifractals. We analyse time series of temperature and in vivo fluorescence taken from a drifter in the mixed coastal waters of the eastern English Channel. Two analysis techniques are used to compute the fundamental universal multifiractal parameters, which describe all the statistics of the turbulent fluctuations: the analysis of the scale invariant structure function exponent ζ(q) and the Double Trace Moment technique. At small scales, we do not detect any significant difference between the universal multifiractal behavior of temperature and fluorescence in an Eulerian framework. This supports the hypothesis that the latter is passively advected with the flow as the former. On the one hand, we show that large scale measurements are Lagrangian and indeed we obtain for temperature fluctuations a ω2 power spectrum corresponding to the theoretical scaling of a Lagrangian passive scalar. Furthermore, we show that Lagrangian temperature fluctuations are multiscaling and intermittent. On the other hand, the flatter slope at large scales of the fluorescence power spectrum points out that the plankton is at these scales a "biologically active" scalar.

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Nonlinear Processes in Geophysics

Tập 3 Số 4

236-246

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